The development of a sustainable route to ammonia production is one of the largest challenges in chemistry. The world's ammonia-based fertilizer is predominantly supplied by the industrial Haber-Bosch process and by the enzymatic nitrogenase process. These two processes are very different. Nitrogenase reduces N2 molecules at ambient conditions using high energy electrons released though the hydrolysis of 16 ATP molecules. The Haber Bosch process, on the other hand, uses H2 molecules with an iron-based catalyst at high temperature (400-500° C.) and high pressure (150-250 bar), conditions, which generally require centralized production. This process alone produces over 150 million metric tons of ammonia each year and consumes over 1% of the entire global energy supply. Due to the use of hydrocarbon reforming to produce the required hydrogen, it also results in the release of over 450 million metric tons of CO2 annually. It would be desirable to develop an alternative, sustainable process capable of employing renewable resources rather than fossil fuels to produce fertilizer locally where it is used.
To this end, attempts have been made to mimic the enzymatic process with molecular complexes, achieving high selectivity under strongly reducing conditions, however the stability of these catalysts is a challenge. Many photochemical and electrochemical routes to ammonia from N2 and H2O using heterogeneous catalysts have been explored. NH3 production and current efficiencies are usually below 1% due to the exceptional stability of the N2 triple bond and due to competition with the hydrogen evolution reaction (HER). Experimentally, some progress has been made by moving to molten salt systems, which have allowed for higher selectivity of ammonia over hydrogen evolution. Fundamentally, however, it remains a challenge to provide protons and electrons at high enough chemical potential to reduce nitrogen without producing substantial amounts of H2.
What is needed is a method and device that provides a lower impact alternative to the industrial standard Haber-Bosch. A method and device that can operate at lower pressure and that can use water rather than hydrogen gas as the hydrogen source to reduce fossil fuel demands to enable localized and sustainable production of ammonia.